Spontaneously grown Ni(OH)2 on iron oxide nanoparticles with enhanced energy storage performance for electrodes of asymmetric supercapacitors

Iron oxide nanoparticles intercalated in Ni(OH)2 nanosheets were prepared in a spontaneous way for the cathode materials of asymmetric supercapacitors. The soluble precursor of Ni(OH)2, Ni(NH3)6(OH)2, was used for growth on α-Fe2O3 nanoparticles. The loading percentages of Ni(OH)2 in the Ni(OH)2–α-Fe2O3 nanocomposites had a great influence on the morphology and size of Ni(OH)2. The composites were characterized by TEM, SEM, ICP-OES, XRD and XPS. The specific capacitance of Ni(OH)2 in the composite can reach 1107 F g−1 at a scan rate of 20 mV s−1, and the specific capacitance of the Ni(OH)2–α-Fe2O3 composite can be up to 376 F g−1 at a scan rate of 5 mV s−1. More importantly, the fabricated Ni(OH)2–α-Fe2O3//AC (activated carbon) asymmetric supercapacitor exhibited energy density and power density of 31.6 W h Kg−1 and 474 W Kg−1, respectively. The cycling performance of the asymmetric supercapacitor was also excellent, and the capacitance retention reached 89.6% after 5000 charge–discharge cycles. Red, blue and yellow LED lights can be lit up with two series of asymmetric supercapacitors, revealing their potential application in energy storage.